Adrenomedullin (AM) is a 52 amino acid amidated peptide hormone originally isolated from adrenal tumors. AM is involved in numerous physiological activities, including vasodilation, angiogenesis, mitogenesis, and anti-microbial functions. As a result, AM actions are related to a wide array of disease states such as heart and pulmonary disease, cirrhosis, cancer, diabetes, sepsis, inflammation and preeclampsia in mammals, including humans. (See, European Patent No. 0 845 036 and U.S. Ser. No. 09/011,922, filed Feb. 17, 1998 to F. Cuttitta et al.).
In clinical studies, patients with chronic congestive heart failure show elevated plasma AM, and these concentrations increase in proportion to the severity of the heart failure along with other hormones known to affect the progression of the disease (J. Kato et al., 1996, J. Clin. Endocrinol. Metab. 81:180-3). Similarly, patients with congenital cyanotic heart disease show elevated plasma AM levels and increased AM uptake in pulmonary circulation (M. Yoshibayashi et al, 1999, Clin. Sci. (Colch.), 1999, 96:543-7). Patients with chronic obstructed pulmonary disease also show significantly raised AM plasma levels (B. Cheung et al., 1997, Clin. Sci. (Colch.) 92:59-62). Accordingly, increased AM (a potent vasodilator) may function as a compensatory mechanism for hypoxaemia (Kato et al., 1996, supra; Yoshibayashi et al., 1999, supra).
Several independent clinical studies have established that patients with liver cirrhosis show elevated circulating AM, and these levels increase with the severity of the illness (E. Fabrega et al., 1997, Am. J. Gastroenterol. 92:1901-4; C. M. Fernandez-Rodriguez et al., 1998, J. Hepatol. 29:250-6; M. Guevara et al., 1998, Gastroenterology 114:336-43; H Kojima et al., 1998, J. Hepatol. 28:840-6). As peripheral vasodilatation has been implicated in the progression of liver cirrhosis, AM may directly participate in the pathogenesis of the disease (Fabrega et al., 1997, supra; Fernandez-Rodriguez et al., 1998, supra; Guevara et al., 1998, supra; Kojima et al., 1998, supra).
Monoclonal antibodies directed to AM have been shown to inhibit tumor cell growth in a concentration-dependent manner, an effect that is reversed with the addition of exogenous AM (M. J. Miller et al., 1996, J. Biol. Chem. 271:23345-51). AM has also been found to be expressed in numerous and diverse cancer cell lines (M. J. Miller et al., 1996, supra), as well as in small and non-small cell lung carcinomas (A. Martínez et al., 1995, Endocrinology 136:4099-105). In addition, AM binds to specific sites on human malignant melanoma cells and exogenous AM stimulates melanoma cell growth (A. Martínez et al., 1997, Endocrinology 138:5597-604). Moreover, cyclic AMP levels in tumor cells increases in the presence of AM (M. J. Miller et al., 1996, supra; K. Takahashi et al., 1997, Peptides 18:1117-24), indicating that AM may act as a autocrine growth factor to promote neoplastic proliferation (M. J. Miller et al., 1996, supra).
It has been demonstrated that AM inhibits insulin secretion in a dose-dependent manner, while neutralizing monoclonal antibodies directed to AM increases insulin release by 5-fold; this effect was reversed by the addition of synthetic AM (A. Martínez, 1996, Endocrinology 137:2626-32). Additionally, intravenous injection of AM reduces the levels of insulin in the bloodstream with a concomitant increase in circulating glucose (Martínez , 1996, supra). These observations implicate AM as an insulin regulatory factor involved in diabetes and obesity.
In clinical experiments, septic patients showed extremely elevated plasma AM concentrations, and those with acute renal failure had markedly elevated plasma AM levels during the early course of the illness; however, AM levels declined rapidly during the recovery course (Y. Hirata et al., 1996, J. Clin. Endocrinol. Metab. 81:1449-53). Similarly, patients with systemic inflammatory response syndrome, pancreatitis, traumatic shock, or severe sepsis show significantly increased plasma levels of AM, and these levels increased in proportion to the severity of illness (S. Ueda et al., 1999, Am. J. Respir. Crit. Care Med. 160:132-6). AM levels also correlate with sepsis markers such as the Acute Physiology and Chronic Health Evaluation II score and the peak multiple organ failure score, indicating that AM levels can be used to evaluate the severity of sepsis and can serve as an early predictor of organ failure and outcome (Ueda et al., 1999, supra).
The diverse actions of AM are thought to be orchestrated by temporal and/or tissue-specific regulatory factors. The activities of several other peptide hormones are modulated by binding proteins present in extracellular fluids. For example, one of the most well characterized classes/families of hormone binding proteins are the insulin-like growth factor binding proteins (IGF-BPs). IGF-BPs can direct, enhance, or block the action of IGF-1 on cells by regulating the ability of IGF-1 to bind to cell surface receptors (D. R. Clemmons et al., 1998, Mol. Cell. Endocrinol. 140: 19-24).
The detection, isolation and identification of AM-binding proteins, or families of such proteins, are therefore important goals for the further understanding of AM regulation and function in both normal and disease states in animals, including mammals, preferably humans. Such AM-binding proteins may stabilize or destabilize AM, direct AM to specific sites, modulate AM-binding to its receptor, or otherwise interact with AM to regulate or modulate its activity and/or function. AM-binding proteins may thereby provide a molecular basis for the actions of AM on different tissues, at different times, and in different illnesses and disease states.
Moreover, as a result of the present invention, AM-binding proteins can be used to quantify plasma AM levels in order to diagnose and/or monitor the presence or progression of diseases which are characterized by altered concentrations of circulating AM. AM-binding proteins can also be used to prevent or treat diseases caused or exacerbated by elevated levels of plasma AM by administrating AM-binding proteins in dosages sufficient to bind to AM and thereby block AM activities or interactions with other components.